diff options
Diffstat (limited to 'third_party/heimdal/lib/hcrypto/libtommath/bn_mp_rshd.c')
-rw-r--r-- | third_party/heimdal/lib/hcrypto/libtommath/bn_mp_rshd.c | 51 |
1 files changed, 51 insertions, 0 deletions
diff --git a/third_party/heimdal/lib/hcrypto/libtommath/bn_mp_rshd.c b/third_party/heimdal/lib/hcrypto/libtommath/bn_mp_rshd.c new file mode 100644 index 0000000..bb8743e --- /dev/null +++ b/third_party/heimdal/lib/hcrypto/libtommath/bn_mp_rshd.c @@ -0,0 +1,51 @@ +#include "tommath_private.h" +#ifdef BN_MP_RSHD_C +/* LibTomMath, multiple-precision integer library -- Tom St Denis */ +/* SPDX-License-Identifier: Unlicense */ + +/* shift right a certain amount of digits */ +void mp_rshd(mp_int *a, int b) +{ + int x; + mp_digit *bottom, *top; + + /* if b <= 0 then ignore it */ + if (b <= 0) { + return; + } + + /* if b > used then simply zero it and return */ + if (a->used <= b) { + mp_zero(a); + return; + } + + /* shift the digits down */ + + /* bottom */ + bottom = a->dp; + + /* top [offset into digits] */ + top = a->dp + b; + + /* this is implemented as a sliding window where + * the window is b-digits long and digits from + * the top of the window are copied to the bottom + * + * e.g. + + b-2 | b-1 | b0 | b1 | b2 | ... | bb | ----> + /\ | ----> + \-------------------/ ----> + */ + for (x = 0; x < (a->used - b); x++) { + *bottom++ = *top++; + } + + /* zero the top digits */ + MP_ZERO_DIGITS(bottom, a->used - x); + + /* remove excess digits */ + a->used -= b; +} +#endif |